Conventional microcontrollers need POR and PSM circuits for their operation. Some microcontrollers also use a low-power LDO to maintain a regulated supply for a standby mode. FIG. 1 shows a power supply system 100 for a prior art microcontroller. The power supply system 100 includes a power supply VBAT that draws a supply voltage/current from an external power supply (e.g., a battery). The VBAT drives a LDO 102 for regulating a high operation power, a LDO2 104 for regulating a low operation power and a voltage reference circuit 112 for generating an internal voltage reference. The LDOs 102 and 104 drive a voltage on an internal supply line (DVDD) of an integrated circuit. The supply line DVDD may be connected to a capacitor 124. The voltage level on VBAT is monitored by a POR 114, PSM 116 and a POR2 118. Each of the POR 114, PSM 116 and POR2 118 compares the VBAT voltage level to a respective threshold value and generates a respective control signal (e.g., por_bat, psm_bat and por2_bat). The POR 114 typically is accurate within a rough resolution, for example, ˜500mV. The POR2 118 normally has a more precise resolution. The digital supply DVDD is internally generated and used to supply power for digital logic 108, memories 110, and an oscillator 106. Sometimes, the oscillator 106 can also be powered by the VBAT.
DVDD is traditionally monitored by POR 120 and PSM 122. Each of POR 120 and PSM 122 compares the DVDD voltage level to a respective threshold value and generates a respective control signal (e.g., por_dvdd and psm_dvdd). In the prior art microcontroller, POR, PSM are typically implemented as comparators to compare the monitored power supply or a divided-down version of it (e.g., VBAT or DVDD) to a reference voltage (e.g., the reference voltage generated by the voltage reference 112 or a reference voltage generated by a resistive divider from the reference voltage generated by the voltage reference 112). During a power down (e.g., low power operation or standby mode operation), the LDO2 104 keeps the DVDD high to preserve the content of the memories.
In a typical power supply system for a microcontroller, these POR, PSM and LDO circuit blocks take an area of as much as 0.3 mm2 and consume almost 1 mA of current at room temperature (e.g., 27° C.). Therefore, the existing technology in power supply system for microcontrollers takes too much room on an integrated circuit (IC) chip and consumes too much power. Accordingly, there is a need in the art for providing a low power consumption and small area power supply system for an IC chip.